Hot press forming apparatus and hot press forming method

ABSTRACT

During the press forming process of forming a blank sheet material while clamping a die on a punch, a trim portion is clamped between a trim holding step and a cut holder in such a state that elastic force of a spring mechanism is being applied on the trim portion. As a press forming operation by the die goes on, the trimming blade is relatively moved along an outer margin of a punch-side forming surface portion while the cut holder opposes elastic force of the spring mechanism by receiving pressing force of the trim holding step so that the trimming blade shears and cuts off the trim portion between the trimming blade and the tip end corner on the outer margin of the punch-side forming surface portion.

The contents of the following Japanese patent application(s) areincorporated herein by reference:

-   -   NO. 2016-214708 filed on Nov. 1, 2016, and    -   NO. PCT/JP2017/004827 filed on Feb. 9, 2017.

BACKGROUND 1. Technical Field

The present invention relates to a hot press forming apparatus thatheats a blank sheet material made of a steel material to an austenizingtemperature and forms and quenches the heated blank sheet material byusing a low-temperature die to form the blank sheet material, and a hotpress forming method using the hot press forming apparatus.

2. Related Art

In a hot press process, a to-be-formed blank sheet material is heated toan austenizing temperature (austenite temperature) from 750° C. to 1000°C. for quenching, and is supplied in the heated state into a die toform. Then, the heated blank sheet material is rapidly cooled andquenched by the low-temperature die at the end of clamping of the die,is transformed into a martensite structure and hardened. For thatreason, according to the hot press process, an independent quenchingprocess is not necessary and a press-formed work with high strength canbe manufactured by low cost. Therefore, the hot press process issuitable for a vehicle body component manufactured by press forming,such as door impact beam or a center pillar of an automobile, and iswidely applied for this reason.

Further, in the hot press process, performing a piercing process on apress formed work or a trimming process on a trim portion that is amargin of the press formed work is required if such a vehicle bodycomponent or the like is to be manufactured. Hardness of the materialgreatly increases by quenching. Therefore, there is a concern that ifthe piercing process or trimming process is applied after quenching theformed work, high residual stress is generated on a sheared sectioncaused by the piercing process or trimming process performed on theformed work, and delayed fracture occurs in the press-formed work afterthe forming.

Here, the problem of the delayed fracture in the press-formed work afterthe forming can be solved by performing laser piercing process or lasertrimming process on the formed work after the quenching.

However, the investment for dedicated laser equipment is necessary forthe laser piercing process or laser trimming process that is performedon the formed work after the quenching. In addition, laser machiningtime is added on its cost. Therefore, this may also make thepress-formed work expensive.

SUMMARY

So, a plural devised hot press forming processing technologies bycompleting the piercing and trimming the blank sheet material in aheated state, that is, an unhardened state have been proposedconventionally to solve the delayed fracture by the laser machining andthe cost-up by investment for dedicated equipment (for example, PatentDocument 1 and Patent Document 2).

As a hot press forming apparatus that realizes the hot press formingprocessing technologies, a hot press forming apparatus that forms thematerial into a shape of the press-formed work having a hat crosssection, for example, is exemplified. As shown in FIG. 5 to FIG. 8, thishot press forming apparatus is configured to have a die including a diea as a mobile type and a punch b as a stationary type. The die a has arecessed fitting portion d that is formed on a center of a die-sideforming surface portion c. Also, the punch b has a raised portion f thatis formed corresponding to the recessed fitting portion d on a center ofa punch-side forming surface portion e. An outer edge portion h of thepunch-side forming surface portion e cooperates with a trimming blade gthat is formed on an outer edge portion of the die-side forming surfaceportion c to configure the trimming tool i.

According to a conventional hot press forming apparatus configured inthis manner, first, as shown in FIG. 5, a blank sheet material j that isheated to an austenizing temperature is supplied between the die-sideforming surface portion c and the punch-side forming surface portion e.

Next, the die a is moved toward the punch b, the recessed fittingportion d of the die-side forming surface portion c is fit in a raisedportion f of the punch-side forming surface portion e to form the blanksheet material j.

To advance the process of forming the blank sheet material j, as the diea is further moved toward the punch b and clamping is performed, asshown in FIG. 6, a protruding portion k is gradually formed in apredetermined shape on the blank sheet material j, and the trimmingblade g of the die-side forming surface portion c abuts on the blanksheet material j.

From the state that the trimming blade g of the die-side forming surfaceportion c abuts on the blank sheet material j in this manner, the die ais further moved toward the punch b side. Accordingly, as shown in FIG.7, the forming of the protruding portion k on the blank sheet material jfurther goes on. In addition, after the blank sheet material j abuts onthe outer edge portion h of the punch-side forming surface portion e, atrim portion m as a margin on a margin of the blank sheet material j isbent by a cooperation of the outer edge portion h and the trimming bladeg, and accordingly, the trimming process starts.

Then, during a process in which the movement of the die a to the punch bfurther goes on, the trim portion m is torn off (fractured) from theblank sheet material j by the cooperation of the trimming blade g andthe outer edge portion h, and the trimming process ends (the state shownin FIG. 8).

After that, in such a state that the blank sheet material j is finallyclamped between the die a and the punch b, the blank sheet material j israpidly cooled by a cooling system not shown in the drawings, andundergoes the quench-hardening process. Accordingly, the blank sheetmaterial j is formed so as to have a hat cross section having aprotruding portion that has a predetermined shape, and a press-formedwork is completed.

Therefore, the conventional hot press forming processing technology isstill a technology of heating a blank sheet material to an austenizingtemperature, forming the heated steel material by a die including thelow-temperature die a and punch b, and quenching the steel material. Inthe conventional hot press forming processing technology, the trimmingprocess by the trimming tool i is performed in such a state that theblank sheet material is unhardened yet during the press forming by thedie.

As a result, because the trimming process performed during the hot pressforming is performed on a blank sheet material that has not undergonethe quench-hardening process in the still high-temperature state, theresidual stress generated on the trimming portion to be cut off can below, thereby making an effect of eliminating the occurrence of thedelayed fracture.

[Patent Document 1] Japanese Patent Application Publication No.2005-248253 [Patent Document 2] Japanese Patent Application PublicationNo. 2011-92946

However, in any of these conventional hot press processing technologies,when the trimming process is to be performed, the trimming process isperformed on the trim portion m that remains in such a state that thetrim portion m is not supported or held by the punch b, that is, remainsin a so-called aerial cutting state.

The trimming process of cutting off the trim portion m by the aerialcutting is performed on the trim portion m that remains in the not-heldstate. As a result, during the process of cutting off the trim portion mby tearing off the trim portion m while the trimming tool I is bendingthe trim portion m, “burrs” are formed on a cut surface present on acomponent of the press-formed work of the blank sheet material j.

Because the pressed product in which the “burrs” are formed in thismanner cannot be supplied for actual use, an operator needs to perform adeburring process as a subsequent process that is performed after thepress forming and that is not included in the press forming process, toremove the burrs.

As a result, for the completed press-formed work, the working man hourincreases caused by the addition of the manual process, which has been areason causing high cost. Because the burrs are also quenched andhardened together with the press-formed work, the deburring process iseven more difficult. This also increases the cost of the press-formedproducts.

Here, the present invention provides a hot press forming apparatus and ahot press forming method that can eliminate the burrs-occurring on thepress-formed work by the trimming process during the hot press formingprocess even with a configuration in which the trimming process isperformed on a high-temperature blank sheet material, which eliminatesthe hand-work process for deburring performed after forming and enablesthe reduction of the processing man-hours and consequently, cost-down ofthe products.

The hot press forming apparatus according to one aspect of the presentinvention may have a press forming apparatus configured to form apre-heated blank sheet material into a shape of a press-formed work byclamping a die having a forming surface portion on a punch having aforming surface portion. The hot press forming apparatus may have a trimportion cut-off apparatus configured to trim a trim portion as a marginbeing a portion of the blank sheet material that is not included in thepress-formed work. The hot press forming apparatus may have aquench-hardening apparatus configured to quench and harden the heatedblank sheet material by rapidly cooling while being clamped between thepunch and the die. The trim portion cut-off apparatus may have a trimholding step formed forward so as to protrude toward the punch at theouter margin of the die-side forming surface portion. The trim portioncut-off apparatus may have a trimming tool that includes a trimmingblade formed on a tip end corner on an inner margin of the trim holdingstep, and a tip end corner formed on the outer margin of the punch-sideforming surface portion. The trim portion cut-off apparatus may have acut holder surrounded the outer margin of the punch-side forming surfaceportion so as to face the trim holding step. The trim portion cut-offapparatus may have a spring mechanism that is provided on the punch andthat supports the cut holder in such a state that the cut holder iselastically energized toward the trim holding step, the cut holder beingmovable closer to/away from the trim holding step. During a pressforming process of forming the blank sheet material while the blanksheet material is clamped between the die and the punch by the pressforming apparatus, the trim portion may be clamped between the trimholding step and the cut holder in such a state that elastic force ofthe spring mechanism is being applied. As the press forming operation bythe die goes on, the trimming blade may be relatively moved along theouter margin of the punch-side forming surface portion while the cutholder opposes elastic force of the spring mechanism by receivingpressing force of the trim holding step so that the trimming blade mayshear and cut off the trim portion between the trimming blade and thetip end corner on the outer margin of the punch-side forming surfaceportion. After the cutting off process of the trim portion by the trimportion cut-off apparatus ends, the quench-hardening apparatus mayquench the blank sheet material by clamping the blank sheet materialbetween the punch and the die finally.

Also, the hot press forming method according to one aspect of thepresent invention is a hot press forming method using the hot pressforming apparatus. The hot press forming apparatus may have a pressforming apparatus configured to form a pre-heated blank sheet materialinto a shape of a press-formed work by clamping the blank sheet materialbetween a die having a forming surface portion and a punch having aforming surface portion. The hot press forming apparatus may have a trimportion cut-off apparatus configured to trim a trim portion as a marginbeing a portion of the blank sheet material that is not included in thepress-formed work. The hot press forming apparatus may have aquench-hardening apparatus configured to quench and harden the heatedblank sheet material by rapidly cooling while the heated blank sheet isclamped between the punch and the die. The trim portion cut-offapparatus may have a trim holding step formed forward so as to protrudetoward the punch at the outer margin of the die-side forming surfaceportion. The trim portion cut-off apparatus may have a trimming toolthat includes a trimming blade formed on a tip end corner on an innermargin of the trim holding step, and a tip end corner formed on theouter margin of the punch-side forming surface portion. The trim portioncut-off apparatus may have a cut holder surrounded the outer margin ofthe punch-side forming surface portion so as to face the trim holdingstep. The trim portion cut-off apparatus may have a spring mechanismthat is provided on the punch and that supports the cut holder in such astate that the cut holder is elastically energized toward the trimholding step, the cut holder being movable closer to/away from the trimholding step. The hot press forming method may include: during a pressforming process of forming the blank sheet material while the pressforming apparatus is clamping the blank sheet material between the dieand the punch, clamping the trim portion between the trim holding stepand the cut holder in such a state that elastic force of the springmechanism is being applied. The hot press forming method may include: asa press forming operation by the die goes on, shearing and cutting off,by the trimming blade, the trim portion between the trimming blade andthe tip end corner on the outer margin of the punch-side forming surfaceportion by causing the trimming blade to relatively move along the outermargin of the punch-side forming surface portion while causing the cutholder to oppose elastic force of the spring mechanism by receivingpressing force of the trim holding step. The hot press forming methodmay include: after the cutting off process of the trim portion by thetrim portion cut-off apparatus ends, quenching, by the quench-hardeningapparatus, the blank sheet material by clamping the blank sheet materialbetween the punch and the die finally.

According to one aspect of the present invention, the cut holder isconfigured to cooperate with the trim holding step to clamp the trimportion, and the spring mechanism is configured to support the springmechanism. Accordingly, as the forming of the blank sheet material goeson, accompanied by the progress of the press forming operation by thedie, the trim holding step presses and moves the cut holder whilecausing the cut holder to oppose elastic force of the spring mechanism.As the process of pressing and moving goes on, the spring mechanism iscontracted, and accordingly, the clamping force to the trim portionbetween the cut holder and the trim holding step is gradually increasedwhile the cut holder increases the reaction force.

According to the above, before the trimming process on the trim portionbefore the final clamping of the die on the punch, because the degree ofcontraction of the spring mechanism is still low and the reaction forceon the cut holder by the spring mechanism is small, the clamping forceon the trim portion between the cut holder and the trim holding step isextremely slight. Therefore, the blank sheet material can be drawn totwo forming surfaces of each of the die and the punch with approximatelyno resistance, and the blank sheet material feed to the two formingsurface portions is not impeded. As a result, the blank sheet materialcan be formed into a desired thickness or a desired shape by the punchand the die, thereby obtaining a desired press-formed work.

Also, as described above, according to one aspect of the presentinvention, the clamping force between the cut holder and the trimholding step before the trim portion is cut off is small because thedegree of expansion/contraction of the spring mechanism is extremelyslight, and the temperature fall by heat dissipation of the pre-heatedblank sheet material is suppressed by clamping the trim portion betweenthe cut holder and the trim holding step. Accordingly, by the earlyhardening of the blank sheet material, that the material cannot be fedto the forming die including the die and the punch can be prevented.Therefore, occurrence of the worst phenomenon such as material crack ofthe blank sheet material can be prevented. Also, a press-formed workhaving desired strength can be formed when the subsequent cooling andquenching is to be performed on the blank sheet material after finallyclamping the blank sheet material between the punch and the die.

According to one aspect of the present invention, at the time of finalclamping of the die on the punch, the trim holding step causes thespring mechanism to be largely contracted according to the clampingoperation by the die, and accordingly, the degree of contraction of thespring mechanism that supports the cut holder becomes high. In responseto this, a large reaction force is generated on the cut holder on thetrim holding step, and the clamping force on the trim portion betweenthe cut holder and the trim holding step extremely increases. As aresult, the blank sheet material before the quench-hardening rightbefore the final forming step is firmly clamped by the cut holder andthe trim holding step. Accordingly, the occurrence of wrinkles oroverlapping of the press-formed works caused by excessive feed of theblank sheet material to the forming surface portions of each of thepunch and the die is suppressed. Also, a shearing process enabling neatfinish with no burr by cutting off the trim portion can be performed onthe press-formed work.

As a result, according to one aspect of the present invention, in thetrimming process that is performed by the trimming blade by cooperatingwith the tip end corner of the punch-side forming surface portion, theso-called aerial cutting, by which the trim portion is torn off whilebeing bent as the prior art, does not occur. Consequently, no burr isformed on the completed press-formed work. Therefore, the deburringprocess performed after the pressed product is completed can beeliminated, thereby achieving the reduction of the processing man-hoursand consequently, the product cost reduction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic longitudinal cross-sectional view illustrating oneexample of a state that a blank sheet material is set at the time ofdie-opening of a die on a punch of a hot press forming apparatusaccording to one embodiment.

FIG. 2 is a schematic longitudinal cross-sectional view illustrating oneexample of a process in the middle of press forming of the blank sheetmaterial in such a state that the blank sheet material is formed byclamping the blank sheet material between the die and the punch from thedie-opening state in FIG. 1 and the trim portion is clamped between thecut holder of the punch and the trim holding step of the die.

FIG. 3 is a schematic longitudinal cross-sectional view illustrating oneexample of a state that the cutting off of the trim portion startsbetween the trimming blade of the die and a tip end corner formed on theouter margin of the punch-side forming surface portion when the clampingof the die on the punch goes on from the state of the process in themiddle of press forming the blank sheet material in FIG. 2.

FIG. 4 is a schematic longitudinal cross-sectional view illustrating oneexample of a state that the clamping of the die on the punch furthergoes on from the state that the shearing and cutting off of the trimportion starts in FIG. 3, and after the trim portion is sheared and cutoff by the trimming blade of the die and the tip end corner formed onthe outer margin of the punch-side forming surface portion, thequenching of the blank sheet material by clamping the blank sheetmaterial between the die and the punch finally is to be performed.

FIG. 5 is a schematic longitudinal cross-sectional view illustrating astate that a blank sheet material is set at the time of die-opening of apunch on a die of a conventional hot press forming apparatus.

FIG. 6 is a schematic longitudinal cross-sectional view illustrating aprocess in the middle of press forming of the blank sheet material byclamping the die on the punch from the die-opening state in FIG. 5.

FIG. 7 is a schematic longitudinal cross-sectional view illustrating astate that the clamping of the die on the punch goes on from the stateof the process in the middle of press forming of the blank sheetmaterial in FIG. 6 and the cutting off of the trim portion starts.

FIG. 8 is a schematic longitudinal cross-sectional view illustrating astate that the clamping of the die on the punch further goes on from thestate that the cutting off of the trim portion starts in FIG. 7, afterthe trim portion is cut off, the quenching of the blank sheet materialby clamping the blank sheet material between the die and the punchfinally is performed.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

According to the hot press forming apparatus and the hot press formingmethod using the apparatus according to an embodiment of the presentinvention, the burrs-occurring on the press-formed work by the trimmingprocess in the hot press forming process is eliminated, therebyeliminating the deburring process performed after the forming andachieving the reduction of the processing man-hours and consequently,the product cost reduction.

Next, the hot press forming apparatus according to an embodiment of thepresent invention is described using FIG. 1 to FIG. 4.

The hot press forming apparatus according to an embodiment of thepresent invention has a die including a die 1 as a mobile type and apunch 2 as a stationary type, similar to the prior art. Then, each ofthe die 1 and the punch 2 has forming surface portions 4, 5 made to forma blank sheet material 3 to be a press-formed work (not shown in thedrawings) presenting a predetermined shape, for example, a hat crosssection.

Here, among the forming surface portions 4, 5, a recessed fittingportion 4 a is formed on a center of the die-side forming surfaceportion 4. On a center of the punch-side forming surface portion 5, araised portion 5 a is formed facing the recessed fitting portion 4 a.The recessed fitting portion 4 a and the raised portion 5 a cooperatewith each other to form the blank sheet material 3 into thepress-formed-work shape being the hat cross section.

Therefore, the die 1 having the die-side forming surface portion 4 onwhich the recessed fitting portion 4 a is formed and the punch 2 havingthe punch-side forming surface portion 5 on which the raised portion 5 ais formed configure a press forming apparatus to form the press-formedwork having the hat cross section.

Also, the trim holding step 6 that protrudes toward the punch 2 isformed forward at the outer margin 4 b of the die-side forming surfaceportion 4. The trimming blade 7 is formed on the tip end corner in aninner margin 6 a of the trim holding step 6. The trimming blade 7 and atip end corner 5 c formed on an outer margin 5 b of the punch-sideforming surface portion 5 configure a trimming tool.

Further, the cut holder 8 is arranged facing the trim holding step 6 andbeing adjacent to the outer margin 5 b of the punch-side forming surfaceportion 5. The cut holder 8 is configured to be movable along the outermargin 5 b of the punch-side forming surface portion 5 by being pressedon the trim holding step 6 accompanied by the forming operation by thedie 1 in such a state that the cut holder 8 is elastically energizedtoward the trim holding step 6 by a spring mechanism 9 provided on thepunch 2. Note that the spring mechanism 9 can be configured by using acoil spring or a pneumatic or hydraulic cylinder.

As a result, during the press forming process, by the press formingapparatus, of forming the blank sheet material 3 while moving the die 1toward the punch 2 and clamping the die 1, the trim holding step 6 andthe cut holder 8 clamp the trim portion 3 a being the margin of theblank sheet material 3 in such a state that the elastic force of thespring mechanism 9 is being applied.

Also, while the trim portion 3 a is kept being clamped by the trimholding step 6 and the cut holder 8, in response to the press formingoperation by the die 1 advancing, the trim portion cut-off apparatuscauses the cut holder 8 to relatively move along the outer margin 5 b ofthe punch-side forming surface portion 5 while causing the cut holder 8to oppose the elastic force of the spring mechanism 9 and applying thepressing force of the trim holding step 6 to the trimming blade 7.Accordingly, the trim portion cut-off apparatus is configured to shearand cut off the trim portion 3 a between the trimming blade 7 and a tipend corner 5 c on the outer margin 5 b of the punch-side forming surfaceportion 5.

The quench-hardening apparatus is configured to: after the trim portioncutting-off process by the trim portion cut-off apparatus ends, quenchthe blank sheet material 3 by clamping the blank sheet material 3between the die 1 and the punch 2 finally and rapidly cooling them byusing a cooling system or the like which is not shown in the drawings.

By using the hot press forming apparatus according to theabove-described embodiment of the present invention, the blank sheetmaterial 3 is formed by the below processes to obtain the press-formedwork. First, as shown in FIG. 1, the blank sheet material 3 heated to anaustenizing temperature is supplied and set between the die-side formingsurface portion 4 of the die 1 that is opened relative to the punch 2and the punch-side forming surface portion 5 of the punch 2.

Next, the die 1 is moved toward the punch 2 and the punch-side formingsurface portion 5 is fit in the recessed fitting portion 4 a of thedie-side forming surface portion 4 to form the blank sheet material 3.

As the die 1 is further moved toward the punch 2 and the clamping isperformed to advance the forming of the blank sheet material 3, aprotruding portion is formed on the blank sheet material 3 by an effectof the recessed fitting portion 4 a and the raised portion 5 a, as shownin FIG. 2. In addition, because the cut holder 8 is flush with thepunch-side forming surface portion 5 or protrudes to the trim holdingstep 6 by the elastic force of the spring mechanism 9, the cut holder 8and the trim holding step 6 receive the elastic force of the springmechanism 9 to clamp the trim portion 3 a being the margin of the blanksheet material 3.

In this manner, as the forming operation on the blank sheet material 3by the die 1 goes on while the trim portion 3 a is kept being clamped bythe cut holder 8 and the trim holding step 6, the cut holder 8 receivesthe pressing force of the trim holding step 6, and is relatively movedalong the outer margin 5 b of the punch-side forming surface portion 5while opposing the elastic force of the spring mechanism 9.

In this manner, the relative movement of the cut holder 8 along theouter margin 5 b of the punch-side forming surface portion 5 goes on andas the cut holder 8 is moved below the tip end corner 5 c of thepunch-side forming surface portion 5 as shown in FIG. 3, the trimmingblade 7 starts shearing the trim portion 3 a of the blank sheet material3 between the punch-side forming surface portion 5 and the tip endcorner 5 c accompanied by this movement.

As the cut holder 8 is moved along the outer margin 5 b of thepunch-side forming surface portion 5 while opposing the elastic force ofthe spring mechanism 9 from the state, the shearing of the trim portion3 a that is kept being clamped between the cut holder 8 and the trimmingtrim holding step 6 goes on. Finally, as shown in FIG. 4, the trimportion 3 a is sheared and cut off from the main body portionconstituting the press-formed work of the blank sheet material 3.

Then, when the cutting off process of the trim portion 3 a ends in thismanner, the die 1 and the punch 2 are finally clamped and are rapidlycooled by the cooling system, and the quenching process of performingquenching on the blank sheet material 3 is performed. Accordingly, thepress-formed work is completed.

As described above, in the above-described embodiment of the presentinvention, the cut holder 8 that cooperates with the trim holding step 6to clamp the trim portion 3 a is supported by the spring mechanism 9.

As the forming of the blank sheet material 3 goes on, the trim holdingstep 6 causes the cut holder 8 to be moved while pressing the cut holder8 opposing the elastic force of the spring mechanism 9 accompanied bythe progress of the press forming operation by the die 1. As themovement along with the pressing goes on, the spring mechanism 9 iscontracted and the cut holder 8 generates the reaction force togradually increase the clamping force on the trim portion 3 a betweenthe cut holder 8 and the trim holding step 6.

According to the above, before the trimming process on the trim portion3 a before the time of the final clamping of the die 1 on the punch 2,the degree of contraction of the spring mechanism 9 is still low and thereaction force on the cut holder 8 by the spring mechanism 9 is small.Accordingly, the clamping force on the trim portion 3 a between the cutholder 8 and the trim holding step 6 is extremely slight. The blanksheet material 3 can be drawn to the forming surface portions 4, 5 ofeach of the die 1 and the punch 2 with approximately no resistance andthe blank sheet material 3 feed to the forming surface portions 4, 5 isnot impeded. By forming the blank sheet material 3 by such punch 2 anddie 1, a press-formed work having a desired thickness or a desired shapecan be obtained.

Also, as described above, according to the embodiment of the presentinvention, because the degree of expansion/contraction of the springmechanism 9 before the trim portion 3 a is cut off is extremely slight,the clamping force between the cut holder 8 and the trim holding step 6is small. Therefore, the pre-heated blank sheet material 3 dissipatesthe heat by clamping the trim portion 3 a by the cut holder 8 and thetrim holding step 6, and the temperature fall can be suppressed fromoccurring. That the material cannot be fed to the forming die configuredwith the die 1 and the punch 2 due to the early hardening of the blanksheet material 3 and the occurrence of the worst phenomenon such as thematerial crack of the blank sheet material 3 can be prevented.Furthermore, the press-formed work having desired strength can be formedwhen the subsequent cooling and quenching is to be performed on theblank sheet material 3 after the final clamping is performed on thepunch 2 and the die 1.

According to the embodiment of the present invention, at the time offinal clamping of the die 1 on the punch 2, the spring mechanism 9 islargely contracted according to the clamping operation by the die 1 onthe trim holding step 6, and accordingly, the degree of contraction ofthe spring mechanism 9 that supports the cut holder 8 becomes high. Inresponse to this, large reaction force on the trim holding step 6 isgenerated on the cut holder 8, and the clamping force on the trimportion 3 a between the cut holder 8 and the trim holding step 6extremely increases. As a result, the blank sheet material 3 beforequench-hardening right before the final forming step is firmly clampedby the cut holder 8 and the trim holding step 6. Accordingly, theoccurrence of the wrinkles or overlapping of the press-formed workscaused by the excessive feed of the blank sheet material 3 to theforming surface portions 4, 5 of each of the punch 2 and the die 1 issuppressed. In addition, a shearing process enabling neat finish with noburr by cutting off the trim portion 3 a can be performed on thepress-formed work.

As a result, according to one aspect of the present invention, in thetrimming process that is performed by the trimming blade 7 bycooperating with the tip end corner 5 c of the punch-side formingsurface portion 5, the so-called aerial cutting by which the trimportion is torn off while being bent as the prior art does not occur.Accordingly, the burrs are not occurred in the completed press-formedwork. Therefore, the deburring process performed after the pressedproduct is completed is eliminated, thereby achieving the reduction ofthe processing man-hours, and consequently the product cost reduction.

INDUSTRIAL APPLICABILITY

According to the above-described one aspect of the present invention,the burrs-occurring on the press-formed work by the trimming processduring the hot press forming process can be eliminated even with aconfiguration in which the trimming process is performed on ahigh-temperature blank sheet material. Accordingly, the deburringprocess performed after forming is eliminated, thereby achieving thereduction of the processing man-hours, and consequently, the productcost reduction. Therefore, for a vehicle body component manufactured bythe press forming, for example, a door impact beam or a center pillar ofan automobile, the hot press forming apparatus of forming by heating ablank sheet material made of a steel material to an austenizingtemperature and forming and quenching the heated steel material by usinga low-temperature die, and the hot press forming method using the hotpress forming apparatus are suitable.

EXPLANATION OF REFERENCES

1 . . . die; 2 . . . punch; 3 . . . blank sheet material; 3 a . . . trimportion; 4 . . . die-side forming surface portion; 4 a . . . recessedfitting portion; 4 b . . . outer margin; 5 . . . punch-side formingsurface portion; 5 a . . . raised portion; 5 b . . . outer margin; 5 c .. . tip end corner; 6 . . . trim holding step; 6 a . . . inner margin; 7. . . trimming blade; 8 . . . cut holder; 9 . . . spring mechanism

What is claimed is:
 1. A hot press forming apparatus comprising: a pressforming apparatus configured to form a pre-heated blank sheet materialinto a shape of a press-formed work by clamping a die having a formingsurface portion on a punch having a forming surface portion; a trimportion cut-off apparatus configured to trim a trim portion as a marginbeing a portion of the blank sheet material that is not included in thepress-formed work; and a quench-hardening apparatus configured to quenchand harden the heated blank sheet material by rapidly cooling whilebeing clamped between the punch and the die, wherein the trim portioncut-off apparatus has: a trim holding step that is formed forward as toprotrude toward the punch at an outer margin of the forming surfaceportion of the die; a trimming tool that includes a trimming bladeformed on a tip end corner on an inner margin of the trim holding step,and a tip end corner formed on an outer margin of the forming surfaceportion of the punch; a cut holder that is arranged adjacent to theouter margin of the forming surface portion of the punch so as to facethe trim holding step; and a spring mechanism that is provided on thepunch and that supports the cut holder in such a state that the cutholder is elastically energized toward the trim holding step, the cutholder being movable closer to/away from the trim holding step, whereinduring a press forming process of forming the blank sheet material whilethe press forming apparatus is clamping the die on the punch, the trimportion is clamped between the trim holding step and the cut holder insuch a state that elastic force of the spring mechanism is beingapplied, as a press forming operation by the die goes on, the trimmingblade is relatively moved along the outer margin of the forming surfaceportion of the punch while the cut holder opposes elastic force of thespring mechanism by receiving pressing force of the trim holding step sothat the trimming blade shears and cuts off the trim portion between thetrimming blade and the tip end corner on the outer margin of the formingsurface portion of the punch, and after the cutting off process of thetrim portion by the trim portion cut-off apparatus ends, thequench-hardening apparatus quenches the blank sheet material by clampingthe blank sheet material between the punch and the die finally.
 2. A hotpress forming method using a hot press forming apparatus, wherein thehot press forming apparatus has: a press forming apparatus configured toform a pre-heated blank sheet material into a shape of a press-formedwork by clamping a die having a forming surface portion on a punchhaving a forming surface portion; a trim portion cut-off apparatusconfigured to trim a trim portion as a margin being a portion of theblank sheet material that is not included in the press-formed work; anda quench-hardening apparatus configured to quench and harden the heatedblank sheet material by rapidly cooling while being clamped between thepunch and the die, wherein the trim portion cut-off apparatus has: atrim holding step that is formed forward so as to protrude toward thepunch at an outer margin of the forming surface portion of the die; atrimming tool that includes a trimming blade formed on a tip end corneron an inner margin of the trim holding step, and a tip end corner formedon an outer margin of the forming surface portion of the punch; a cutholder that is arranged adjacent to the outer margin of the formingsurface portion of the punch so as to face the trim holding step; and aspring mechanism that is provided on the punch and that supports the cutholder in such a state that the cut holder is elastically energizedtoward the trim holding step, the cut holder being movable closerto/away from the trim holding step, and the hot press forming methodcomprises: during a press forming process of forming the blank sheetmaterial while clamping the die on the punch by the press formingapparatus, clamping the trim portion between the trim holding step andthe cut holder in such a state that elastic force of the springmechanism is being applied; as a press forming operation by the die goeson, shearing and cutting off, by the trimming blade, the trim portionbetween the trimming blade and the tip end corner on the outer margin ofthe forming surface portion of the punch by causing the trimming bladeto relatively move along the outer margin of the forming surface portionof the punch while causing the cut holder to oppose elastic force of thespring mechanism by receiving pressing force of the trim holding step;and after the cutting off process of the trim portion by the trimportion cut-off apparatus ends, quenching, by the quench-hardeningapparatus, the blank sheet material by clamping the blank sheet materialthe punch and the die finally.